smith - flow interactions and control - spring review 2012

1 DISTRIBUTION A: Approved for public release; distribution is unlimited. 9 March 2012

Integrity Service Excellence

Dr. Douglas Smith

Program Manager

AFOSR/RSA

Air Force Research Laboratory

Flow Interactions and

Control

08 MAR 2012

2 DISTRIBUTION A: Approved for public release; distribution is unlimited.

2012 AFOSR SPRING REVIEW

NAME: Douglas Smith

BRIEF DESCRIPTION OF PORTFOLIO:

Foundational research examining aerodynamic interactions of

laminar/transitional/turbulent flows with structures, rigid or flexible,

stationary or moving.

Fundamental understanding is used to develop integrated control

approaches to intelligently modify the flow interaction to some advantage.

LIST SUB-AREAS IN PORTFOLIO:

Flow Physics for Control

Flow Control Effectors

Low Reynolds Number Unsteady Aerodynamics

Aeromechanics for MAVs


Inspiration …

Parameter boundaries

HIGH

Turbulent Flow • Disorderly, but

asymptotic

LOW

Laminar Flow • Smooth & orderly

Transition

Affected by … • Roughness • Freestream

turbulence


Inspiration …

Disciplinary boundaries

CNT wire array

Novel Materials

Biology Energy

Chemical Interactions

Flow Physics

for

Control

Unsteady

Low Rey

Aero

Scientific Challenges

Flow

Control

Flow

Control

Fluid-

Structure

Interaction

DISTRIBUTION A: Approved for public release; distribution is unlimited


Opportunities …

• Create opportunities in Gust tolerance/mitigation Agility Hover Integrated lift & thrust

• Reconfigurable aircraft • Coordinated flight, swarming • Drag reduction, Enhanced

efficiency

Require an understanding of aerodynamic-structure

interactions and control.

Flow Physics

for

Control

Unsteady

Low Rey

Aero

Scientific Challenges

Flow

Control

Flow

Control

Fluid-

Structure

Interaction

DISTRIBUTION A: Approved for public release; distribution is unlimited..

Key to Lines

Portfolio map

Flow Physics for

Control

Flow Control

Flow Control

Future Work

Unsteady Low Rey

Aero

Fluid- Structure

Interaction

Flow Control

Wygnanski Fasel

Glezer

Graham

Gregory

Spedding

Mahesh

Little

Karagozian

YIP

Sodano Morris Sondergaard Leishman MURI LRIR

Hubner

Lang

Ifju

Bernal OL

Eldredge Edwards

Gopalarathnam

Ringuette

Buchholz

Jones

Rockwell

Gursul

Gordnier

Visbal

Koochesfahani

YIP

YIP

YIP

LRIR

LRIR

LRIR

Mittal

Hedrick

Thomson

Deng

Williamson

Snyder

Sytsma

Breuer

Dong

Golubev

Swartz

Rempfer

Wark

Shkarayev

LRIR

Cattafesta

Ukeiley

Alvi

Cybyk

Rowley

Williams

Colonius

Thurow

Flow control collaboration

Flow physics & Control

Applied flow control

Low Reynolds number unsteady aerodynamics

Flight physics for MAVs PI Co-PI 2012 New Start

Bio-inspiration


Exploiting the nonlinear dynamics of near-wall

turbulence for skin-friction reduction M. Graham, Wisconsin

• Drag in many aerodynamic flows is dominated by

near-wall turbulent flow structures • Approaches to skin-friction reduction often focus on

manipulation of these structures via suction/blowing or topography (riblets)

• In liquids, dramatic changes in these structures and corresponding high levels of drag reduction (>70%) can be achieved by adding long-chain polymers.

• Recent discoveries: • polymer stresses suppress normal “active”

turbulence” but do not affect intervals of “hibernating” turbulence that exhibit very low skin friction,

• hibernating turbulence intervals are found occasionally even without polymer additives.

⇒Goal: Exploit these observations to develop new

boundary control schemes to make these low-drag intervals more frequent and thus reduce overall drag in aerodynamically important flows.

Background and objective Recent results

Active

Hibernating

vorticity

velocity

Laminar flow

Turbulent

flow Upper branch ECS

Low-drag excursions-

hibernation

Turbulent bursts

Basin boundary:

• lower-branch ECS

• edge state

Initial condition

that becomes

turbulent

Initial condition

that becomes

laminar

High-drag active

turbulent dynamics

Proposed schematic of the state space dynamics of turbulent wall-bounded flow.

dra

g


Control of boundary-layer separation for lifting surfaces H. Fasel, Arizona

Profiles of time-averaged u-velocity

Simulation

Experiment

0.027 m/s

0.054 m/s

0.087 m/s

separation bubble

reattachment

Investigating the transition process of separation bubbles in the presence of freestream turbulence

• Experimental observations description of bubble behavior

• Simulations require that freestream turbulence is included to predict exp observation


1) Investigate nonlinear interactions between

these phenomena

2) Leverage nonlinear interactions for

effective control strategies

12

1 2 3 4 5 6 7 8 9 100.5

5

50

Mode index

En

erg

y c

onte

nt

(%)

SB mode (15.2% energy)

Wake (11.7% energy)

POD

2 4 6 8 10 12 14

106

105

104

f

λn·

v

SB/wake mode (f = 4.45)

SL mode (f = 8.90)

Spatial harmonic (f = 13.34)

Koopman

SL mode (2.99% energy)

Wednesday, November 23, 2011

St » 0.26

St » 0.53

SIMULATED EXPERIMENTAL

DYNAMICAL ANALYSIS

Fixed frequency structures similar Oscillating structures

AN INTEGRATED STUDY OF SEPARATION CONTROL L. Cattafesta (FSU), R. Mittal (JHU), & C. Rowley (Princeton)

Reattached separation (bubble)

Detached separation

• Investigation into nonlinear coupling of stalled airfoil

• Shear layer probe reveals quadratic coupling nonlinear coupling between shear layer and wake instabilities

EXPERIMENTS

a =12°


Rotorcraft Brownout – Advanced Understanding Control

and Mitigation G. Leishman, Maryland


Rotorcraft Brownout – Advanced Understanding Control

and Mitigation G. Leishman, Maryland

Summary of the six sediment mobilization, uplift, and suspension

mechanisms observed from a bed below a rotor: creep; modified

saltation, vortex-induced trapping, unsteady suction pressure

effects, secondary suspension, particle bombardment/splash

• Rotor wake dynamics “in ground effect” is at the root of the problem

• Unsteady, 2-phase, 3-dimensional fluid dynamics problem

• Wake impinging on the ground creates:

– Transient excursions in flow velocities

– Unsteady shear stresses and pressures

– Secondary vortical flows and local regions of flow separation

– Turbulence

Simulated dust clouds using a Lagrangian free-vortex rotor

wake method and Lagrangian sediment particle tracking

method (~1012 particles) along with contours of induced

velocity on the ground (note high 3-dimensionality) for a

dynamic simulation of a helicopter landing over a surface

covered with a sediment bed


Lense-let array

Development of a Compact and Easy-to-Use 3-D

Camera For Measurements in Turbulent Flow Fields B Thurow, Auburn

Near Mid Far

Conventional

imaging

Plenoptic

imaging

Conventional 2-D Imaging Systems 2-D information neglects inherent 3-D nature of turbulent flows Camera integrates angular information, which leads to depth-of-field and blur Reduced aperture (restricted angular information) leads to low signal levels

Lightfield Imaging Plenoptic camera records both the position and angle of light rays that enter the camera Eliminates the need for complex, expensive multi-camera arrangements Dense sampling of 3-D scene

Portfolio map

Flow Physics for

Control

Flow Control

Flow Control

Future Work

Unsteady Low Rey

Aero

Fluid- Structure

Interaction

Flow Control

Wygnanski Fasel

Glezer

Graham

Gregory

Spedding

Mahesh

Little

Karagozian

YIP


Hubner

Lang

Ifju

Bernal OL

Eldredge Edwards

Gopalarathnam

Ringuette

Buchholz

Jones

Rockwell

Gursul

Gordnier

Visbal

Koochesfahani

YIP

YIP

YIP

LRIR

LRIR

LRIR

Mittal

Hedrick

Thomson

Deng

Williamson

Snyder

Sytsma

Breuer

Dong

Golubev

Swartz

Rempfer

Wark

Shkarayev

LRIR

Cattafesta

Ukeiley

Alvi

Cybyk

Rowley

Williams

Colonius

Thurow





Flight physics for MAVs

Key to Lines

PI Co-PI 2012 New Start

Bio-inspiration


Biological Inspiration

Courtesy of Breuer & Swartz, Brown


Challenges & Questions

Unsteady, periodic flow-fields

Laminar-transitional flows

CHALLENGES QUESTIONS

To what extent can the flow be

treated as quasi-steady?

Three-dimensional flow-fields Can the flow be treated as 2-D

along the span of the wing? What

can we learn from these 2-D

treatments?

Low Reynolds number flows How good are inviscid

approximations?

Wing flexibility What is the role of flexibility in

modifying aerodynamic efficiency?

Wing kinematics How sensitive are the aerodynamics

to the kinematics? Rectilinear vs

flapping?

How well must these flows be

resolved?

Separation & Leading-edge vortices Why separated flow? Do LEVs

have universal formation scaling?


Visbal, AFRL/Rockwell, Lehigh

Bio-Inspired Aerodynamics

HIGH

LOW

Starting/stopping transients

Leading edge vortex formation

Universal scaling

3D/wing tip effects

Transition to turbulence

3D aero-elastic, dynamic flight

Neuro-physiological control

Evolutionary biology

Ringuette, SUNY-Buffalo

Hubner et al, Alabama

Rigid Wing

Aerodynamics

OL, AFRL

Hi-fidelity

Simulations

Aerodynamics

&

Flexibility Surface flexibility/compliance

Flow induced vibrations

Natural, passive flow control

Gordnier, AFRL

Source: Wikimedia Commons

Snyder, AFRL

Wing Structure

Wood Harvard

Bio-Inspired

Flight

Breuer/Swartz et al, Brown

MURI07

18


From Gliding to Powered Flight

Onychonycteris finneyi

•What pressures led from passive gliding to powered flight?

•What is the role passive wing deformation or motion in

biological flight?

50 million years ago bats evolved from gliding to powered

flapping flight. BUT…

stationary

self-excited

oscillations


Effect of Membrane Flexibility on Leading Edge

Separation R Gordnier, AFRL/RBAC

Membrane Flexibility:

Reduces the extent of leading

edge separation

Enhances lift at the cost of

increased L/D

Reduces nose down pitching

moment

CL CD L/D Cmy

Rigid-Flat 0.965 0.235 4.112 -0.160

Rigid-Cambered 1.020 0.269 3.794 -0.140

Flexible

Membrane

1.024 0.262 3.903 -0.122

Rigid, Flat Wing Rigid,

Cambered Wing

Flexible Wing


Control of Low Reynolds Number Flows with Fluid-

Structure Interactions I Gursul, Bath

Objectives:

(i) exploit fluid-structure interactions to delay stall and increase lift of airfoils and wings at low Reynolds numbers

(ii) improve maneuverability and gust response of MAVs.

Approach:

(i) simulate aerolastic vibrations by means of small-amplitude plunging oscillations of airfoils and wings

(ii) develop flexible wings based on this knowledge.

Rectangular

b/c=2 Elliptical

b/c=2

Elliptical

b/c=1

Rectangular

b/c=1

a

b

c

d

a

b

c

d


Flapping-Wing Vortex Formation and Scaling M. Ringuette (YIP 2010), Buffalo

• TV flow anchors

LEV to plate,

prevents shedding

• Colors indicate flow

along vortices

• Tip vortex effect

insufficient to anchor

LEV, observe

shedding & eventual

breakdown of vortex

structure

AR=2, =48° AR=4, =48°

θCCDcamera

Plate

Laser

Not to scale

Top view

Stage

Objective …

• find a scaling parameter connecting the vortex formation/strength to the kinematics, which should relate to

important force features if a formation-parameter scaling holds

Approach …

• characterize the general 3-D vortex topology

• track how the vortex loop evolves in space and time

• find the effects of non-dimensional parameters such as AR, Rossby no., on strength, vortex loop stability


Three-dimensional Vortex Formation On A Pitching

Wing D. Rockwell (Lehigh) & M. Visbal (AFRL/RBAC)

Experiments Simulations

Vortex structure

Surface pressure


High-Resolution Computational Studies and Low-Order

Modeling of Agile Micro Air Vehicle Aerodynamics J. Eldredge, UCLA

RAPID PITCH-UP

High-fidelity results Low-order model streamlines

Lift vs Angle of Attack

Drag vs Angle of Attack

OBJECTIVES • Develop low-order phenomenological models (< ~10 dof for flapping wing flight, • Examining a progression of canonical wing motions, with both rigid and flexible wings. • Simultaneously explore the physics of canonical wing motions using high-fidelity numerical simulations.

MAIN ACHIEVEMENTS • Constructed a low-order model based on point vortex dynamics • Successfully demonstrated that model captures force generated by a 2-d flat plate in pitch-up • High-fidelity simulation requires ~1,000,000 degrees of freedom; low-order model requires only 6


Albatross

Energy Extraction From Unsteady Winds Williams (IIT)/ Colonius (Caltech)

How? … DYNAMIC SOARING!!

Extracting energy from spatial velocity gradients in the wind.

Williams/Colonius

• Investigate unsteady and nonlinear phenomena relevant

to gusts over wings

• Without flow control can extract energy from flow

• Integrate active closed-loop flow with flight control

• Demonstrate benefits of increased range and

endurance by extracting energy from gusting flows

U+wx

tilted L Lo

apparent Ta

Wz

D OR

Lee of an ocean swell

Wz

L D

Up-gust

½ cycle

Down-gust

½ cycle

Wind gust

Model gliders flying at 400+ mph!!

Albatross remains aloft indefinitely!

25


Future …

Tomorrow

Today

Transformational Computing in

Aerospace Science & Engineering To create transformational approaches in computing for aerospace

science and engineering. “How can we exploit quantum computing architectures specifically to

advance aerospace computing?”

Applications of QC in Aerospace S&E Meyer et al, UCSD

Quantum Speedup for Turbulent Combustion Simulations

Givi et al, Pitt

PMs: Drs. Douglas Smith & David Stargel, RSA Partners: Drs. Curcic, Fahroo, Luginsland

H sim Fourier X-form

Phase

est.

Ampl

amplif

QA

L y = x

Investigate QC improvements in… 1. Solving systems of ODEs 2. Optimization of (non)smooth fcns 3. Evolving the gnd state of a

molecule

LES of Turbulent

Reacting Flows

Resolved large scales

SGS model

FDF SDE

• Develop quantum sim techniques for stochastic diff eqs (SDEs)

Portfolio map

Flow Physics for

Control

Flow Control

Flow Control

Future Work

Unsteady Low Rey

Aero

Fluid- Structure

Interaction

Flow Control

Wygnanski Fasel

Glezer

Graham

Gregory

Spedding

Mahesh

Little

Karagozian

YIP


Hubner

Lang

Ifju

Bernal OL

Eldredge Edwards

Gopalarathnam

Ringuette

Buchholz

Jones

Rockwell

Gursul

Gordnier

Visbal

Koochesfahani

YIP

YIP

YIP

LRIR

LRIR

LRIR

Mittal

Hedrick

Thomson

Deng

Williamson

Snyder

Sytsma

Breuer

Dong

Golubev

Swartz

Rempfer

Wark

Shkarayev

LRIR

Cattafesta

Ukeiley

Alvi

Cybyk

Rowley

Williams

Colonius

Thurow





Flight physics for MAVs

Key to Lines

PI Co-PI 2012 New Start

Bio-inspiration

smith - flow interactions and control - spring review 2012

Technology